All of the prior art discovered by search in the U.S. Patent and Trademark Office is as follows:
______________________________________ U.S. Pat. No. Patentee Granting Date ______________________________________ 889,883 E. J. Johnson June 2, 1908 1,233,232 A. H. Heyroth July 10, 1917 1,334,485 C. D. Clipfell et al Mar. 23, 1920 1,352,960 A. H. Heyroth Sept. 14, 1920 1,894,357 G. Manikowske et al Jan. 17, 1933 1,944,239 H. Honnef Jan. 23, 1934 2,144,719 H. Geffcken Jan. 24, 1939 3,740,565 N. G. Wesley June 19, 1973 ______________________________________
The field of search was
U.S. Class 290, subclasses 43, 44, 54, 55 PA1 U.S. Class 415, subclasses 2,4 PA1 U.S. Class 416, subclasses 3, 90A, 197A